The latter is a storage facility, and only occasionally open. Tours of the The British Postal Museum Store are run on the afternoon of the first Wednesday of the month, for those who can do Wednesday afternoons, but weekend access is much rarer. Yesterday's Open Day, entitled Pillar Box Perfection, was therefore a special opportunity to get inside.Access is by car, close to junction 5 of the M11, or you can walk from Debden station at the far end of the Central line. The Museum Store is housed in a very ordinary-looking grey warehouse by the railway, very close to the building where the Bank of England prints our banknotes.

What a lot of stuff... but then, when you stop and think about all the things the Royal Mail has needed to do over the years, that's perhaps not surprising. First up by the door are a selection of phone boxes, just to get the telephone thing out of the way. The rest of the room is taken up with accoutrements for the delivery of mail, of which there are many. Let's start with Pillar Box Alley.

Britain's first pillar boxes were installed on Jersey in 1853, courtesy of novelist-to-be Anthony Trollope. They soon spread to the mainland, in a variety of styles, most of which can be seen here down 'Pillar Box Alley'. Many are beautiful, especially the early designs, one especially ostentatious version painted green with gold acanthus leaves. Scotland's Suttie box had an ostentatious crown on the top, while the city of Liverpool was granted special dispensation for an especially large box with a chunky lock to improve security. Much of the story of the early years is of gradual design optimisation. It took a while to realise that slots facing upwards caused the mail inside to get wet when it rained. It took a little longer to decide that horizontal slots were harder to steal mail out of than vertical. But before long beauty combined with practicality, and the sentinels of our street corners were set.I hadn't realised before quite how deeply the foundations of certain pillar boxes are buried in the ground. But I guess they need to be, else any old reprobate with a JCB could come along and wrench the box out of the ground and whisk it away. I doubt they'd find much of value in a pillar box today, but the booty haul would once have been quite considerable.

The archetypal Victorian box was the Penfold, hexagonal and elegant with a leafy design on top. A number of these survive around the country (including just down the road from Little Holland House in Carshalton Beeches, damn, missed that). Indeed Royal Mail attempts to keep all its historicboxes in situ, so there might be a rare survivor down your street. Most of the boxes we see today have their origin in 1879's "Anonymous" pillar box, so called because the sovereign's name was initially omitted from the front. Pillar Box Alley also includes a pair of boxes featuring Edward VIII's monogram and a bright blue Air Mail depository, right up to modern oval doubles and futuristic rounded stumps. Even better we had the Museum Store's guides to tell us about some of the designs in great detail, but you had to hang around for quite some time to hear the full story.If you're thinking "ooh, pillar boxes, fascinating" you might be interested in joining the Letter Box Study Group, "the acknowledged authority on the history and development of the British roadside letter box", who for £23 a year will keep you updated on the heritage of these fine objects.

Elsewhere...

The little machines they used to sell stamp books out of.

Racks of pigeonholes used for sorting mail into.

Mini postboxes of the kind found embedded in walls.

An elegant leather desk for writing telegrams on.

Two machines used to convert postcodes into patterns of dots on envelopes.

And, ooh, a Mail Rail train. If you're not aware, a mini underground railway used to run between Paddington and Whitechapel purely for the transference of mailbags [map]. I was even taken to see it once in the 1970s, as a very special treat, and remember the rattling of the trains as they vanished off through the low tunnel portal. The trains look a little bigger above ground, with chunky locomotives of a sit-on-able size at each end and a few trucks inbetween. Mail Rail closed in 2003 because high-volume cross-London transport was no longer needed, and may one day be opened up as a tourist attraction, but will more likely crumble.

According to the BPMA Twitter feed, just over 150 visitors passed through the doors of the Museum Store today. They're very pleased with those numbers, indeed they received only 249 visitors during the whole of the previous financial year. But Londoners (and Essexites) I'm very disappointed in you. Less than 0.002% of you thought to turn up today, despite advancepublicity, even though rather more of you would have enjoyed it. Alas there isn't yet a publicised date for the next truly open day, but watch out for those Wednesday afternoon tours if you're interested. Or hang on until the newPostal Museum is opened at Mount Pleasant, hopefully in 2016, and make sure you visit that.You might also enjoy reading the Postal Heritage blog, or delving through their comprehensively large collection of Online Exhibitions.